| John Barr | |
| Riding1: | Dufferin |
| Parliament1: | Canadian |
| Term Start1: | 1904 |
| Term End1: | 1909 |
| Predecessor1: | New riding |
| Successor1: | John Best |
| Office2: | Ontario MPP |
| Term Start2: | 1898 |
| Term End2: | 1902 |
| Predecessor2: | William Dynes |
| Successor2: | John Roaf Barber |
| Term Start3: | 1890 |
| Term End3: | 1894 |
| Predecessor3: | Falkner Cornwall Stewart |
| Successor3: | William Dynes |
| Term Start4: | 1875 |
| Term End4: | 1879 |
| Predecessor4: | New riding |
| Successor4: | William Jelly |
| Constituency4: | Dufferin |
| Party: | Conservative (Ontario), (1875-1902) |
| Otherparty: | Conservative (Canada), (1904-1909) |
| Birth Date: | 4 March 1843 |
| Birth Place: | Elizabethtown, Canada West |
| Occupation: | Physician |
John Barr (March 4, 1843 - November 19, 1909) was an Ontario-based Canadian physician and political figure. He represented Dufferin in the Legislative Assembly of Ontario from 1875 to 1879, from 1890 to 1894 and from 1898 to 1904 and in the House of Commons of Canada from 1904 to 1909 as a Conservative member. From 1890 to 1894, he was a member of the provincial Conservative Equal Rights Party.
He was born near Elizabethtown (later Brockville) in Canada West in 1843, the son of Irish immigrants. He graduated as an M.D. from Victoria University in 1866. Barr served as an associated coroner for Grey County. He was Deputy Master in the South Grey County Orange Lodge. Barr first set up practice in Horning's Mills but later moved to Shelburne. In 1880, he married Ermina E. Palmer. After being reelected in 1879, he was unseated after an appeal. He was later reelected several times to the provincial and federal assemblies. He died in office in 1909.